1. Field of the Invention
The invention concerns an installation for spraying a coating product such as a paint or a varnish at a controlled flowrate: it proposes improvements for controlling accurately the flowrate of said coating product during a spraying phase and the quantity stored without there being any risk of the coating product circulation means or the means for measuring the flowrate or the quantity stored being damaged by said product. It is more particularly concerned with an installation of this type enabling the coating product to be changed very quickly.
2. Description of the Prior Art
To coat objects satisfactorily by spraying a finely divided coating product, in particular automatically, it is desirable continuously to adapt the flowrate of the coating product feeding the sprayer to the surface area to be covered per unit time. For example, in the case of an automobile body moving at constant speed past sprayers that are fixed or scanned with a more or less complex motion, the flowrate of the coating products must be lower, other things being equal, when painting the door columns than when painting larger surfaces such as hoods or roofs, for example. Consequently, the paint flowrate should ideally be modifiable at will at any time during a spraying phase. Also, the quantity of paint needed to paint a given object may vary according to the color of the paint. In a known color changing system in which the quantity of paint needed to paint one object or a group of objects a particular color is stored temporarily in an intermediate storage tank, the two-fold problem usually arises of monitoring the paint flowrate during the spraying phase and of metering the necessary quantity of paint to be fed into the intermediate storage tank before the spraying phase.
This type of installation with intermediate storage tank(s) constitutes an attractive solution in the case of electrostatic application of electrically conductive coating products, such as certain metallic paints or water-based paints. It is then easier to insulate electrically the intermediate storage tank and the sprayer from other subsystems that are necessarily grounded during a spraying phase in which the sprayer is necessarily at a high voltage.
Numerous installations with intermediate storage tank(s) for electrostatic or other application are known. French patent application No 2 572 662 may be cited by way of example.
In this kind of context it is possible to control the flowrate of the coating product and its variations and also, where applicable, the metering of the coating product fed into an intermediate storage tank, using a computer. The flowrate monitoring and/or metering means must offer high performance and must be reliable. When these means (pumps, flowrate regulators, flowrate sensors, etc) are inserted into coating product circulation circuits they must offer very high performance, and are therefore expensive, if the required reliability and durability are to be achieved. The following phenomena are particularly relevant:
The product to be sprayed may be abrasive and/or chemically aggressive. Consequently, precision devices for metering and monitoring the flowrate such as pumps, gear-type sensors and pressure regulators must be capable of resisting the action of such products.
The product to be sprayed may be a non-Newtonian liquid (this is the case with some water-based paints in particular). In this case monitoring the flowrate by monitoring the pressure on the upstream side of a calibrated nozzle is not possible. Other means must therefore be used, such as pumps and/or gear-type sensors, which are particularly sensitive to the nature of the product flowing through them (in particular its abrasive characteristics). The problem becomes difficult to solve when it is required to implement electrostatic application of a water-based paint with fast color changes as one is faced simultaneously with problems of metering, insulation and the use of a relatively abrasive product.